The integration of viral DNA into the host cells'chromosomes is a required step in the retroviral infection process. Though a fairly detailed understanding of the catalytic function of retroviral integrase has been obtained through in vitro studies, little is known about the role of these enzymes in nuclear entry and targeting to cellular chromatin in vivo. Recent work from the sponsor's laboratory has identified a nuclear localization signal (NLS) in the integrase protein of avian sarcoma virus (ASV) (Kulkolj et al., 1996). The broad goal of research in this proposal is to gain an increased understanding of the manner in which retroviruses may use intracellular trafficking mechanisms to gain access to nuclear DNA targets for integration. The biological significance of the ASV IN NLS will be investigated using two complementary approaches. In the first specific aim, a nuclear import assay with semipermeabilized cells will be employed to investigate the mechanism of IN-mediated import into the host cell nucleus. This assay will also facilitate the isolation and characterization of specific cytosolic components that associate with the ASV IN NLS. In the second specific aim the effects of mutations in the ASV IN NLS on viral growth kinetics and subcellular distribution of preintegration complexes will be investigated. Knowledge of the details of cellular trafficking as they apply to integration will provide broader insight into the pathogenesis of retroviruses, some of which are known to cause cancer and immunodeficiencies, such as AIDS.